I found a better example of what I want to do :

http://blog.jdsarchitects.com/   just click on the image at the left side.

thank you.

I've tried adding that line but my gallery background isn't transparent yet.
I also tried adding 'opacity:x' to the body rule inside index.html but that seems to make the images transparent, not the background.
Could that be because I'm using AV Pro 1.3? If yes, what would be the code for 1.3?

Yes, I added that line and cleared the cache but the background is still solid grey.
My gallery can be found here.
Also, if I can really make the background transparent, is there a way to edit the amount of transparency?

I removed the background-color and the background is white when I launch index.html from my computer, while it's still gray on my website.
I also tried background-color:transparent with no luck (makes background white in local but still grey on web). Adding opacity:x would make images transparent, as I said before.

So how can I make this HTML transparent?
What if I link to the .swf? I tried that too, but it doesn't load the images.

What transparency do you mean? Would you mind showing me a screenshot? I mean, the shadowbox gives transparency AROUND the gallery (which is surrounded by a thin white border), but the background of the gallery itself isn't transparent at all yet. I'd like see my page through the background.